The present invention relates to a data management system, and more particularly, to a data management system that continuously enlarges and reduces a memory area without stopping the system. Further, the present invention relates to a memory device used in a data management system and a program storage medium that form a continuous memory area from a plurality of interconnected memory devices.
In a computer system, an extremely large and continuous memory area is often needed to store a large volume of data, such as for dynamic images. However, the connection of a single memory device to a computer may not be sufficient for obtaining the required large and continuous memory area. Redundant Array of Inexpensive Disks (RAID), in which a plurality of memory devices are connected to a computer to form a single memory area, has thus been proposed. With reference to FIG. 1, in a RAID system, a plurality (e.g., four) of memory devices (volumes) 11, 12, 13, 14 are arranged and configured as a single memory device (volume) 15 in order to disperse and store data in the plurality of volumes 11-14 and increase the processing speed.
In a disk system employing RAID, when the memory capacity is insufficient, a memory device is added during operation of the system. Then, the data stored in the original memory device is transferred to the added memory device and reorganized. In case there is surplus memory area, the data stored in the memory devices 11-14 are transferred to a further RAID disk system and reorganized. One of the memory devices 11-14 (e.g., memory device 12) is then disconnected from the others.
In this manner, although a RAID disk system enables the memory capacity to be enlarged and reduced without stopping operation of the system, data must be reorganized. Accordingly, it takes time for the RAID disk system to perform such memory management functions. Further, during such transfer and reorganization of data, data read and write operations are prohibited. This complicates control of the system.
In addition, if the memory devices have different capacities, the capacity of each memory device cannot be used efficiently. For example, referring to FIG. 2, when employing four memory devices 16, 17, 18, 19 having different memory capacities, the full area of the memory device 16, which has the smallest capacity, and the area in each of the memory devices 17-19 equal to the capacity of the memory device 16 form a first volume 20. The remaining area of the memory devices 18, 19 and the remaining area of the memory device 17 equal to the remaining areas of the memory devices 18, 19 form a second volume 21. The final remaining area of the memory device 17 forms a third volume 22.
The four memory devices 16-19 are then managed as the three volumes 20-22. In this case, the memory capacity of the first volume 20 is smaller than the total memory capacity of the four memory devices 16-19. In other words, a volume that includes the entire capacity of all of the memory devices 16-19 is not formed. This decreases the operational efficiency of the memory devices.
It is an object of the present invention to provide a method for controlling a memory device that facilitates enlargement and reduction of a memory area and efficiently uses plural memory devices.
To achieve the above object, the present invention provides a method for controlling a plurality of memory devices connected to a system. Each of the memory devices has a memory area. The method includes determining for each of the memory devices whether it is designated for forming a continuous memory area, and forming a single continuous memory area from the memory areas of the designated memory devices.
A further aspect of the present invention provides a data management system including a plurality of memory devices, each having a memory area. A controller determines whether each of the memory devices is usable for forming a continuous memory area and forms a single continuous memory area from the memory areas of the usable memory devices.
Another aspect of the present invention provides a computer-readable storage medium storing a program for controlling a plurality of memory devices in a data management system. Each memory device has a memory area. The program includes determining whether each of the memory devices is usable to form a continuous memory area using the memory area of the memory device, and forming a single continuous memory area from the memory areas of the usable memory devices.
A further aspect of the present invention provides a memory device having a memory area connectable to a system that forms a single continuous memory area using memory areas of a plurality of memory devices. The memory device includes a memory unit for storing management information indicating whether the memory device is usable for forming part of the continuous memory area.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.